Method of sealing lead-in conductors



Oct. 29, 1946. c GOQDALE METHOD OF SEALING LEAD-IN CONDUCTORS Filed May 27, 1942 *INVENTOR Patented Get. 29, 1946 METHOD OF SEALING LEAD-IN CONDUCTORS Lynn 0. Goodale, Newark, N. 3., assignor to Federal Telephone and Radio Corporation, a

corporation of Delaware Application May 27, 1942, Serial No. 444,664

Claims. 1

This invention relates to metal-to-glass seals and more particularly to seals for vacuum tube lead-in conductors.

In lead-in conductors for vacuum tubes it has been found that the glass seal to the lead-in conductor externally of the tube should be of such a form that the glass has a reentrant cusp portion or invert at the point of sealing to theconductor. This has generally been accomplished by forming a glass head on the conductor with the invert formation and then sealing the glass flare to this beading without destroying the condition at the conductor. This invert is not deirable with copper conductors, but has been found desirable for common types of lead-in conductors such as tungsten.

It is an object of my invention to provide a simple method for sealing lead-in conductors to a glass flare arrangement without necessitating the special formation of the beads, as required in the prior art.

In accordance with a feature of my invention a lead-in conductor is provided with a glass bead which need not be especially formed with a reentrant part or invert. is then sealed to this bead. This sealing is accomplished by arranging the conductor within a tubular extension on the flare arrangement so that the bead is supported at a point below the upper end of this extension. The glass is then heated to soften it and as it droops inwardly due to the softening first contacts and seals to the bead about the wire and then further falls inwardly to complete a seal to the part of the bead adjacent the wire and will inherently have the desired invert.

A better understanding of my invention may be had by the particular description thereof made with reference to the accompanying drawing, in which Fig. 1 illustrates a tube base plate or flare;

Fig. 2 a beaded conductor; and

Figs. 3, 4 and 5, various steps in the completion of the seal.

In Fig. 1 is shown a tube base or lead-in flare arrangement H1, provided with tubular extending portions II and I2, all substantially identical in form. The shape of these extensions may be more readily seen by reference to Fig. 3.

Extensions II are generally used for lead-in seals, while extension I2 may be used for the connection of an exhaust tube for exhausting the completed vacuum tube.

The lead-in conductor, for example of tungsten, is shown at l3, Fig. 2, and is provided with a The tube base or flare glass bead it formed with an enlarged portion 15 at one end thereof. The glass bead 14- may be formed by arranging a small tube on the lead and melting it to seal thereto and then winding on the tubular bead another glass portion, which is then shaped by a graphite paddle or other means to produce the enlarged portion l5.

Lead-in conductor I3 is then arranged. to extend through the extension ll so that the portion l5 of bead i4 is positioned slightly below the upper end l6 of flare H. The work may be supported in a jig for this purpose and it should be understood that all of the lead-in conductors may be simultaneously supported in a similar position with relation to all of the tubular extensions II of the flare.

Heat is then applied to the upper portion of tubular extension ll causing the glass to soften. As this glass softens it droop inwardly and first contacts and seals to the enlarged portion [5 of the bead I l. Figure 4 illustrates the softened glass when it has softened sufficiently to nearly contact the enlarged portion l5 on bead M. A further heating of the glass causes a further softening so that the upper edge It droops further in and finally contacts to conductor l3 at a point just above bead Hi, and seals to the upper surface of said .bead, as can be clearly seen in. Fig. 5.

It will be seen that the completed seal thus has an invert H at the place where it contacts to lead-in conductor l3. The glass, however, doe not seal the conductor at this point, the glass seal with the conductor being solely formed by the bead.

By the use of the method described herein fabrication of tubes may be greatly simplified since it is not necessary to specially form the bead hi on the wire to produce the reentrant cusp-like arrangement.

The invention is particularly useful for all types of lead-in conductors for vacuum tubes, although itis clear that the principles of my invention apply anywhere where rods of the type described are to be sealed to glass, and the form of reentrant or invert seal is desired. It should be distinctly understood that the features of my invention apply to any system wherein a rod is to be sealed through a glass. Furthermore, while its tubular extensions i l are shown to be slightly frusto-conical in form and this shape is generally desirable, the principles of my invention apply as well if the tube is made perfectly straight sided. It is only necessary than when the tubular extension is heated the walls thereof will tend to flow inwardly instead of outwardly of the tubular portion so that it will flow against the outer edge of the bead and then later, the conductor and seal to the remaining upper portion of the bead.

It is to be distinctly understood that while the above description sets forth a specific example of my invention, this description is not intended to limit the scope thereof, but is given merely by way of a preferred example.

What I claim is:

1. The method of sealing a lead-in conductor through a glass wall, comprising positioning a linear conductor having a glass bead sealed around it intermediate its ends, along the axis of an open tubular extension formed in the glass wall, so that a central portion of said tubular extension encircles a central portion of the bead, With an end portion of the extension projecting beyond the adjacent end portion of the bead, heating said tubular extension until said central portion thereof is fused to that of said bead, and

continuing said heating until said end portion of saidtubular extension falls inwardly on that of the bead sealing thereto and forming an annular trough of cusp shape contacting said conductor where said conductor emerges from the bead.

, V2. The method according to claim 1 wherein said bead has an enlarged central portion extending to the end of the bead.

l 3. The method of sealing a lead-in conductor through a glass wall, comprising positioning a linear conductor having previously a glass bead sealed around it intermediate its ends, said bead having an enlarged portion at one end thereof, so'that said conductor extends along the axis of an open tubular extension formed in the glass 4 wall, with the enlarged end of said bead below the free end of said tubular extension and inside thereof, heating said tubular extension adjacent said enlarged portion so that it is fused thereto,

and continuing said heating so that the free end of said tubular extension falls inwardly toward said bead sealing to the upper part thereof, contacting said conductor annularly where it emerges from said head, and inverting at the point of contact with said conductor.

4. The method according to claim 3 wherein said tubular extension is frusto-conical in form narrowing toward its free end, and said enlarged end of the bead is substantially the diameter of the smaller opening of said frusto-conical exten- S1011.

5. The method of sealing a lead-in conductor through a glass wall, comprising positioning a rod having a glass bead sealed around it intermediate its ends, along the axis of an open tube formed in said glass wall of frustoeconical shape narrowing toward its free end, said bead having a cylindrical end portion smaller in diameter than the free end of said frusto-conical tube but large enough to be fused to the tube when the latter is heated, supporting said rod in a position such that said end portion is below the free end of said frusto-conical tube, heating said tube at the upper end thereof until the softened glass drops inwardly first sealing to the outer edges of said glass bead, and then to the upper portion of said contact with said rod. 7

LYNN C. GOODALE. 

